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THE EYE

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          THE EYE

       Bushong Ch. 29 p 358 - 359
    Appendix #1 State Fluoro Syllabus
                          pg 77

       Reference: Ch. 14 Carltons
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    Early Fluoroscopy
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    The eyes are the window to the soul……….
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Red goggles for dark adaptation




    •Fluoroscopy was performed
    •in total darkness
    •so the eyes had to be adjusted
    •for 20 - 30 minutes by wearing red goggles
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• FOVEA CENTRALIS
• CENTRAL PART OF
  RETINA
• CONES TIGHTLY
  PACKED
• REMAINDER –
  CONES DIMISH =
  MORE RODS
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            Human Vision
• Light passes through the lens, where light
  is focused onto the retina.
• Between the cornea and the lens is the
  iris, which acts like a camera diaphragm =
  controls the amount of light admitted into
  the eye
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                the retina
• The retina is important because it
  contains the rods and cones.

• The sharpest point of vision is located in
  the center in an area called the fovea
  centralis.
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                RETINA
• contains millions of specialized
  photoreceptor cells called rods and cones
• That convert light rays into electrical
  signals that transmitted to the brain
  through the optic nerve.
• Rods see in dim light and
• Cones provide the ability to see in color
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            Visual Physiology
        2 types of light receptors
     RODS            CONES
 • NIGHT VISION      •   DAYLIGHT
 • SCOTOPIC          •   PHOTOPIC
 • PERCEIVE GRAYS    •   PERCIEVE COLOR
 • PERIPHERY OF      •   CENTER OF RETINA
   RETINA = DIM      •   BETTER VISUAL
   OBJECTS SEEN          ACUITY
   BETTER – 1000 X
   MORE SENSITIVE
                     New II much brighter
 • 30 min dark
   adaptation
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                The rods
• These are located at the periphery of the
  retina
• There are fewer of them and they are
  sensitive to low levels of light.
• Night vision (scotopic vision) uses the rods
  of the eye to see
• The rods are colorblind
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               The cones
• Cones are located at the center of the
  retina in the fovea centralis
• They respond to intense light levels. As
  such, these are used for our daylight
  (phototropic vision).
• Cones have better visual acuity and better
  contrast perception.
• Cones perceive color
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      Eat the ice cream
                  CONE
     in the DAYLIGHT!
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     Macula & Fovea centralis
• The macula, located in the center of the retina,
  is where most of the cone cells are located.
• The fovea, a small depression in the center of
  the macula, has the highest concentration of
  cone cells.
• The macula is responsible for central vision,
  seeing color, and distinguishing fine detail.
• The outer portion (peripheral retina) is the
  primary location of rod cells and allows for night
  vision and seeing movement and objects to the
  side (i.e., peripheral vision).
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                   CORNEA
• The cornea is a thin transparent protective
  covering that protects the eye.
• It has no blood vessels and it helps focus light
  onto the retina
• Light rays bounce off all objects. If a person is
  looking at a particular object, such as a tree,
  light is reflected off the tree to the person's eye
  and enters the eye through the cornea
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                       IRIS
• located between the cornea and the lens
• colored part of the eye
• It controls the amount of light that is admitted to
  the eye by dilating or constricting the pupil.
• Bright light causes contraction of the iris
  allowing only a small amount of light to hit the
  pupil
• In dim light, the pupil enlarges to allow more
  light to enter the eye.
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                                             IRIS



 • The structure which gives the "color" to
   the eye.
 • The pupil is the hole in the iris.
 • Contraction of the iris makes a pupil
   small.
 • Relaxing of the iris makes the pupil large.
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            LENS & PUPIL
• focuses the light that passes through the
  pupil onto the retina where the light
  receptors are located
• The pupil is the opening to the eye. As the
  iris opens and closes, it causes the pupil
  to dilate or contract.
• Light has to pass through the pupil to
  reach the retina
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                       VISUAL ACUITY

• ABILITY TO PERCEIVE FINE DETAILS
• INTEGRATION TIME = 0.2 SEC (how
  long it takes to identify something)
• Photopic acuity is 10 x greater than
  scotopic
• Contrast perception is our ability to detect
  differences in brightness
• Normal viewing distance 12 – 15 inches
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            Binocular vision
• is the best we can see at and is 12-15 inches
  from the object we are looking at.
• We have a blind spot at about 9 inches and can’t
  see from the periphery of the eye.
• Remember… integration time: 0.2 sec. and it is
  the ability to see and recognize everything we
  will
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                       VISION
•    EYE SEES 32 SHADES OF GRAY
•    COMPUTER 256 – 8 bit to 1024 12 bit depth SHADES
•    REGARDING CINE:
•    32 FRAMES SOME FLICKER (OLD MOVIES)
•    60 FRAMES = NO FLICKER
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     The Eyes & Radiation Dose
• What is the allowable annual limit for the
  eyes? _______________________



• What problems with the eyes were seen
  with early Radiologists?
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     The Eyes & Radiation Dose
• Cataracts (cataractogenic effects)
                           P49 RAD – RHB SYLLABUS

• Formation of Cataracts – dose of several 110
  rads
• Fibers in lens of eye are specialized to transmit
  light
• Damage to these (particularly to the developing
  immature cells – can result in cataracts)
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     Now your turn..
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           The Early years
• Because of the high dose to the patient
  and to the operator’s eyes, radiation
  damage was noted shortly after the
  invention.
• Thomas Edison noted that his vision was
  deteriorating because of the radiation.
• The possibilities of this new find
  outweighed the dangers.
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     •CATARACS
     •Dangers of early fluoro
     •DOSE RESPONSE ??
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